This invention is heat-curable silicone rubber compositions. More particularly, this invention is heat-curable silicone rubber compositions that cure rapidly to give very mechanically strong, nondiscoloring silicone rubber.
The silicone rubber compositions known as millable silicone rubbers as a general rule cure in the presence of organoperoxide and heat to give highly heat-resistant, highly weather-resistant silicone rubbers that have excellent electrical properties, and this good property set has resulted in the frequent use of these compositions in applications where these properties are critical. This notwithstanding, a drawback to silicone rubber compositions of this type has been their slow cure rate. There have already been attempts at raising the cure rate of these silicone rubber compositions. For example, Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 9-95612 (95,612/1997) teaches a cure rate-enhancing method in which dimethylsiloxy-endblocked dimethylsiloxane-methylhydrogensiloxane copolymer is blended into a silicone rubber composition that can be cured by 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.
However, the silicone rubber moldings afforded by this method have a pronounced tendency to stick to the mold or die and thus suffer from poor mold-release properties. Thick silicone rubber moldings prepared by this method also fail to undergo cure in all sections, which prevents the production of silicone rubber moldings of uniform mechanical strength.
As a result of extensive investigations directed to solving the problems described above, the inventors discovered that these problems could be solved by the admixture of a specific type of carbosiloxane dendrimer into organoperoxide-curing silicone rubber compositions. More specifically, the object of the present invention is to provide a heat-curable silicone rubber composition that cures rapidly to give very mechanically strong, nondiscoloring silicone rubber.